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          LV19-01-音频应用-01-ALSA基础知识
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<details class="folding-tag" blue><summary> 点击查看使用工具及版本 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center" rowspan="5">PC端开发环境</td>        <td align="center" width=150px>Windows</td>        <td align="left">Windows11</td>    </tr>    <tr>        <td align="center">Ubuntu</td>        <td align="left">Ubuntu20.04.6的64位版本（一开始使用的是16.04版本，后来进行了升级）</td>      </tr>    <tr>        <td align="center">VMware® Workstation 17 Pro</td>        <td align="left">17.0.0 build-20800274</td>      </tr>    <tr>        <td align="center">终端软件</td>        <td align="left">MobaXterm(Professional Edition v23.0 Build 5042 (license))</td>    </tr>    <tr>        <td align="center">Win32DiskImager</td>        <td align="left">Win32DiskImager v1.0</td>      </tr>    <tr>        <td align="center" rowspan="3">Linux开发板环境</td>        <td align="center">Linux开发板</td>        <td align="left">正点原子 i.MX6ULL Linux 阿尔法开发板</td>      </tr>    <tr>        <td align="center">uboot</td>        <td align="left">NXP官方提供的uboot，NXP提供的版本为uboot-imx-rel_imx_4.1.15_2.1.0_ga(使用的uboot版本为U-Boot 2016.03)</td>      </tr>    <tr>        <td align="center">linux内核</td>        <td align="left">linux-4.15(NXP官方提供)</td>      </tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看本文参考资料 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="5">官方网站</td>        <td align="left"><a href="https://www.arm.com/" target="_blank">https://www.arm.com/</a></td>        <td align="left">ARM官方网站，在这里我们可以找到Cotex-Mx以及ARMVx的一些文档</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/" target="_blank">https://www.nxp.com.cn/ </a></td>        <td align="left">NXP官方网站</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxpic.org.cn/" target="_blank">https://www.nxpic.org.cn/</a></td><td align="left">NXP 官方社区</td>    </tr>    <tr>        <td align="left"><a href="https://u-boot.readthedocs.io/en/latest/" target="_blank">https://u-boot.readthedocs.io/en/latest/</a></td><td align="left">u-boot官网</td>    </tr>    <tr>        <td align="left"><a href="https://www.kernel.org/" target="_blank">https://www.kernel.org/</a></td><td align="left">linux内核官网</td>    </tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看相关文件下载 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="4">NXP</td>        <td align="left"><a href="https://github.com/nxp-imx" target="_blank">https://github.com/nxp-imx</a></td>        <td align="left">NXP imx开发资源GitHub组织，里边会有u-boot和linux内核的仓库</td>    </tr>    <tr>        <td align="left"><a href="https://elixir.bootlin.com/linux/latest/source" target="_blank">https://elixir.bootlin.com/linux/latest/source</a></td>        <td align="left">在线阅读linux kernel源码</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/linux-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga" target="_blank">nxp-imx/linux-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga</a></td>        <td align="left">NXP linux内核仓库tags中的rel_imx_4.1.15_2.1.0_ga</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/uboot-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga" target="_blank">nxp-imx/uboot-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga</a></td>        <td align="left">NXP u-boot仓库tags中的rel_imx_4.1.15_2.1.0_ga</td>    </tr>    <tr>        <td align="center" rowspan="2">I.MX6ULL</td>        <td align="left"><a href="https://www.nxp.com.cn/docs/en/data-sheet/IMX6ULLIEC.pdf" target="_blank">i.MX 6ULL Applications Processors for Industrial Products</a></td>        <td align="left">I.MX6ULL 芯片手册（datasheet，可以在线查看）</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/webapp/Download?colCode=IMX6ULLRM&lang_cd=zh" target="_blank">i.MX 6ULL Applications ProcessorReference Manual</a></td>        <td align="left">I.MX6ULL 参考手册（下载后才能查看，需要登录NXP官网）</td>    </tr></table>
              </div>
            </details>

<h1 id="一、alsa简介"><a href="#一、alsa简介" class="headerlink" title="一、alsa简介"></a><font size=3>一、alsa简介</font></h1><h2 id="1-alsa是什么？"><a href="#1-alsa是什么？" class="headerlink" title="1. alsa是什么？"></a><font size=3>1. alsa是什么？</font></h2><p>ALSA 是 Advanced Linux Sound Architecture（高级的 Linux 声音体系） 的缩写，目前已经成为了 linux下的主流音频体系架构， 提供了音频和 MIDI 的支持，替代了原先旧版本中的 OSS（开发声音系统）。</p>
<p> ALSA 是 Linux 系统下一套标准的、先进的音频驱动框架， 那么这套框架的设计本身是比较复杂的， 采用分离、分层思想设计而成，具体的在应用编程这部分就不需太深入去了解了。</p>
<h2 id="2-官网在哪？"><a href="#2-官网在哪？" class="headerlink" title="2. 官网在哪？"></a><font size=3>2. 官网在哪？</font></h2><p>官网这里：<a target="_blank" rel="noopener" href="https://www.alsa-project.org/wiki/Main_Page">AlsaProject (alsa-project.org)</a>：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917110241585.png" alt="image-20240917110241585" style="zoom:50%;" />

<h2 id="3-alsa基本框架与API"><a href="#3-alsa基本框架与API" class="headerlink" title="3. alsa基本框架与API"></a><font size=3>3. alsa基本框架与API</font></h2><p>在应用层， ALSA 为我们提供了一套标准的 API，应用程序只需要调用这些 API 就可完成对底层音频硬件设备的控制， 如播放、录音等， 这一套 API 称为 alsa-lib。   </p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917110427549.png" alt="image-20240917110427549" style="zoom:50%;" />

<h1 id="二、alsa-lib"><a href="#二、alsa-lib" class="headerlink" title="二、alsa-lib"></a><font size=3>二、alsa-lib</font></h1><h2 id="1-alsa-lib库简介"><a href="#1-alsa-lib库简介" class="headerlink" title="1. alsa-lib库简介"></a><font size=3>1. alsa-lib库简介</font></h2><p>alsa-lib 是一套 Linux 应用层的 C 语言函数库， 为音频应用程序开发提供了一套统一、标准的接口，应用程序只需调用这一套 API 即可完成对底层声卡设备的操控，如播放与录音。  </p>
<p>用户空间的 alsa-lib 对应用程序提供了统一的 API 接口，这样可以隐藏驱动层的实现细节，简化了应用程序的实现难度、无需应用程序开发人员直接去读写音频设备节点。学习ALSA音频应用编程其实就是学习 alsa-lib 库函数的使用、如何基于 alsa-lib 库函数开发音频应用程序。  </p>
<h2 id="2-相关文档"><a href="#2-相关文档" class="headerlink" title="2. 相关文档"></a><font size=3>2. 相关文档</font></h2><p>ALSA 提供了关于 alsa-lib 的使用说明文档，其链接地址为：<a target="_blank" rel="noopener" href="https://www.alsa-project.org/alsa-doc/alsa-lib/">ALSA project - the C library reference: Index, Preamble and License (alsa-project.org)</a>：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917110821775.png" alt="image-20240917110821775" style="zoom:50%;" />

<p>alsa-lib 库支持功能比较多， 提供了丰富的 API 接口供应用程序开发人员调用， 根据函数的功能、作用将这些 API 进行了分类， 可以点击上图中 Modules 按钮查看其模块划分， 如下所示：  </p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917110920722.png" alt="image-20240917110920722" style="zoom:50%;" />

<p>一个分类就是一个模块（module），有些模块下可能该包含了子模块，例如上图中，模块名称前面有三角箭头的表示该模块包含有子模块。</p>
<blockquote>
<ul>
<li>Global defines and functions： 包括一些全局的定义，如函数、宏等；</li>
<li>Constants for Digital Audio Interfaces： 数字音频接口相关的常量；</li>
<li>Input Interface： 输入接口；</li>
<li>Output Interface： 输出接口；</li>
<li>Error handling： 错误处理相关接口；</li>
<li>Configuration Interface： 配置接口；</li>
<li>Control Interface： 控制接口；</li>
<li>PCM Interface： PCM 设备接口；</li>
<li>RawMidi Interface： RawMidi 接口；</li>
<li>Timer Interface： 定时器接口；</li>
<li>Hardware Dependant Interface： 硬件相关接口；</li>
<li>MIDI Sequencer： MIDI 音序器；</li>
<li>External PCM plugin SDK： 外部 PCM 插件 SDK；</li>
<li>External Control Plugin SDK： 外部控制插件 SDK；</li>
<li>Mixer Interface： 混音器接口；</li>
<li>Use Case Interface： 用例接口；</li>
<li>Topology Interface： 拓扑接口。</li>
</ul>
</blockquote>
<p>可以看到， alsa-lib 提供的接口确实非常多、 模块很多，但是这里我们仅涉及到三个模块下的 API 函数，包括： PCM Interface、Error Interface 以及 Mixer Interface。  </p>
<h2 id="3-重要模块"><a href="#3-重要模块" class="headerlink" title="3. 重要模块"></a><font size=3>3. 重要模块</font></h2><h3 id="3-1-PCM-Interface"><a href="#3-1-PCM-Interface" class="headerlink" title="3.1 PCM Interface  "></a><font size=3>3.1 PCM Interface  </font></h3><p>PCM Interface，提供了 PCM 设备相关的操作接口，譬如打开&#x2F;关闭 PCM 设备、配置 PCM 设备硬件或软件参数、控制 PCM 设备（启动、暂停、恢复、写入&#x2F;读取数据） ，该模块下还包含了一些子模块（<a target="_blank" rel="noopener" href="https://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html">ALSA project - the C library reference: PCM Interface (alsa-project.org)</a>） ：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917141725576.png" alt="image-20240917141725576" style="zoom:50%;" />

<p>点击模块名称可以查看到该模块提供的API接口有哪些以及相应的函数说明 。</p>
<h3 id="3-2-Error-handling"><a href="#3-2-Error-handling" class="headerlink" title="3.2 Error handling  "></a><font size=3>3.2 Error handling  </font></h3><p>该模块提供了关于错误处理相关的接口，譬如函数调用发生错误时，可调用该模块下提供的函数打印错误描述信息。 （<a target="_blank" rel="noopener" href="https://www.alsa-project.org/alsa-doc/alsa-lib/group___error.html">ALSA project - the C library reference: Error handling (alsa-project.org)</a>）</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917170629440.png" alt="image-20240917170629440" style="zoom:50%;" />

<h3 id="3-3-Mixer-Interface"><a href="#3-3-Mixer-Interface" class="headerlink" title="3.3 Mixer Interface  "></a><font size=3>3.3 Mixer Interface  </font></h3><p>提供了关于混音器相关的一系列操作接口，譬如音量、 声道控制、增益等等。  （<a target="_blank" rel="noopener" href="https://www.alsa-project.org/alsa-doc/alsa-lib/group___mixer.html">ALSA project - the C library reference: Mixer Interface (alsa-project.org)</a>）</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240917170758907.png" alt="image-20240917170758907" style="zoom:50%;" />

<h1 id="三、alsa-utils"><a href="#三、alsa-utils" class="headerlink" title="三、alsa-utils"></a><font size=3>三、alsa-utils</font></h1><h2 id="1-alsa-utils简介"><a href="#1-alsa-utils简介" class="headerlink" title="1. alsa-utils简介"></a><font size=3>1. alsa-utils简介</font></h2><p>alsa-utils是基于alsa-lib以及Kernel ALSA的一系列工具包，包含测试、配置声卡的工具，例如：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">alsactl, aconnect, alsamixer, amidi, amixer, aplay, aplaymidi, arecord, arecordmidi,</span><br><span class="line">aseqnet, iecset, speaker-test</span><br></pre></td></tr></table></figure>



<h1 id="四、alsa相关节点"><a href="#四、alsa相关节点" class="headerlink" title="四、alsa相关节点"></a><font size=3>四、alsa相关节点</font></h1><h2 id="1-dev-snd-目录中的文件"><a href="#1-dev-snd-目录中的文件" class="headerlink" title="1. &#x2F;dev&#x2F;snd 目录中的文件 "></a><font size=3>1. &#x2F;dev&#x2F;snd 目录中的文件 </font></h2><p>在 Linux 内核设备驱动层、基于 ALSA 音频驱动框架注册的 sound 设备会在&#x2F;dev&#x2F;snd 目录下生成相应的设备节点文件，如 ALPHA I.MX6U 开发板出厂系统&#x2F;dev&#x2F;snd 目录下有如下文件：  </p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">ls -alh /dev/snd</span><br></pre></td></tr></table></figure>

<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918074702600.png" alt="image-20240918074702600" style="zoom:50%;" />

<p>从上图可以看到有如下设备文件：  </p>
<blockquote>
<ul>
<li>controlC0： 用于声卡控制的设备节点， 譬如通道选择、 混音器、 麦克风的控制等， C0 表示声卡 0（card0）；</li>
<li>pcmC0D0c： 用于录音的 PCM 设备节点。其中 C0 表示 card0，也就是声卡 0；而 D0 表示 device0，也就是设备 0；最后一个字母 c 是 capture 的缩写，表示录音；所以 pcmC0D0c 便是系统的声卡0 中的录音设备 0；</li>
<li>pcmC0D0p： 用于播放（或叫放音、回放）的 PCM 设备节点。其中 C0 表示 card0，也就是声卡 0；而 D0 表示 device 0，也就是设备 0；最后一个字母 p 是 playback 的缩写，表示播放； 所以 pcmC0D0p便是系统的声卡 0 中的播放设备 0；</li>
<li>pcmC0D1c： 用于录音的 PCM 设备节点。对应系统的声卡 0 中的录音设备1；</li>
<li>pcmC0D1p： 用于播放的 PCM 设备节点。对应系统的声卡 0 中的播放设备 1。</li>
<li>timer： 定时器。</li>
</ul>
</blockquote>
<h2 id="2-proc-asound-目录下的文件"><a href="#2-proc-asound-目录下的文件" class="headerlink" title="2. &#x2F;proc&#x2F;asound 目录下的文件  "></a><font size=3>2. &#x2F;proc&#x2F;asound 目录下的文件  </font></h2><p>编写的应用程序，虽然是调用 alsa-lib 库函数去控制底层音频硬件，但最终也是落实到对 sound设备节点的 I&#x2F;O 操作，只不过 alsa-lib 已经帮我们封装好了。在 Linux 系统的&#x2F;proc&#x2F;asound 目录下，有很多的文件，这些文件记录了系统中声卡相关的信息，如下所示：  </p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">cd /proc/asound</span><br><span class="line">ls -alh</span><br></pre></td></tr></table></figure>

<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918074945691.png" alt="image-20240918074945691" style="zoom:50%;" />

<h3 id="2-1-proc-asound-cards"><a href="#2-1-proc-asound-cards" class="headerlink" title="2.1 &#x2F;proc&#x2F;asound&#x2F;cards   "></a><font size=3>2.1 &#x2F;proc&#x2F;asound&#x2F;cards   </font></h3><p>通过”cat &#x2F;proc&#x2F;asound&#x2F;cards”命令,查看 cards 文件的内容，可列出系统中可用的、注册的声卡，如下所示：  </p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">cat /proc/asound/cards</span><br></pre></td></tr></table></figure>

<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918075059341.png" alt="image-20240918075059341" style="zoom:50%;" />

<p>imx6ull板子上只有一个声卡（WM8960 音频编解码器），所以它的编号为 0，也就是 card0。系统中注册的所有声卡都会在 &#x2F;proc&#x2F;asound&#x2F; 目录下存在一个相应的目录，该目录的命名方式为 cardX（X 表示声卡的编号），如上面图中的 card0。 card0 目录下记录了声卡 0 相关的信息，如声卡的名字以及声卡注册的 PCM 设备，如下所示：  </p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918075154802.png" alt="image-20240918075154802" style="zoom:50%;" />

<h3 id="2-2-proc-asound-devices"><a href="#2-2-proc-asound-devices" class="headerlink" title="2.2 &#x2F;proc&#x2F;asound&#x2F;devices  "></a><font size=3>2.2 &#x2F;proc&#x2F;asound&#x2F;devices  </font></h3><p>通过查看 &#x2F;proc&#x2F;asound&#x2F;devices 节点，可以列出系统中所有声卡注册的设备，包括 control、 pcm、 timer、 seq 等等。 </p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">cat /proc/asound/devices</span><br></pre></td></tr></table></figure>

<p>如下所示：  </p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918075252721.png" alt="image-20240918075252721" style="zoom:50%;" />

<h3 id="2-3-proc-asound-pcm"><a href="#2-3-proc-asound-pcm" class="headerlink" title="2.3 &#x2F;proc&#x2F;asound&#x2F;pcm  "></a><font size=3>2.3 &#x2F;proc&#x2F;asound&#x2F;pcm  </font></h3><p>查看&#x2F;proc&#x2F;asound&#x2F;pcm节点可以列出系统中的所有 PCM 设备，包括 playback 和 capture： </p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">cat /proc/asound/pcm</span><br></pre></td></tr></table></figure>

<p>如下图所示：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV03-%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91/LV19-01-%E9%9F%B3%E9%A2%91%E5%BA%94%E7%94%A8-01-ALSA%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86/img/image-20240918075327050.png" alt="image-20240918075327050" style="zoom:50%;" />

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